Prosecutors in Siena have been questioning former managers in recent days over allegations that the bank overpaid for the Italian bank Antonveneta, which it purchased for euro9.3 billion from Spanish bank Santander in 2007. The bank, informally known as Montepaschi, also is being investigated for three trades that are expected to cost it hundreds of millions of euros.

Established in 1472, the bank is the world's oldest running financial institution. Its board met for six hours Wednesday but ended the session without releasing a statement.